Lime
sticks extremely well to the surface of the straw bales, and chicken wire is therefore
not required as it is when using a cement stucco. Portland cement will not stick
well to the bale surface and chicken wire must be used and in fact is required
by most building codes. Lime plaster perhaps mixed with adobe plaster is more durable and waterproof than adobe alone. Straw and lime (also straw and adobe) have been used together for centuries
-- marriages made in heaven.

Lime retards the growth of mould (a serious problem in straw bale homes if there
are any moisture problems). Portland cement will not retard the growth of mould.

Lime is somewhat breathable (letting air and moisture pass through the wall) and
will therefore let moisture escape out of the wall if it gets trapped in the bales.
Portland cement is not breathable, thus trapping the mosture which then rots the
bales away.

A
lime stucco was shot professionally on all interior wall surfaces of our
straw bale house... a base coat and a finish coat on two sucessive days. (The
adobe plaster on the external walls which was applied by hand took over a year,
and we just didn't have the time or the energy to do it again on the inside.)

NOTE: A
small amount of Portland Cement was added to increase
drying/curing time. Lime plaster takes a minimum of two to three weeks to cure
otherwise. Since we were under time constraints and had to shoot the walls within
a two day weekend, adding approximately 20%cement (one to five ratio of cement
to lime) produced sufficient drying/curing that the second finish coat could be
applied within 24 hours. Only a small amount of cement was added to the final
coat. Adding more than 20% cement is not recommended as it significantly decreases
the breathability of the stucco which is so crucial for straw bale walls.

White cement was used since coloring added later to the finished walls will
take and cover better than over the grey of the more common form of Portland cement.

The surface was lightly trowelled for the right texture
using a float sponge. The light tan coloring of the plaster was achieved by adding
Ferrous Sulfate powder (a soil additive obtained from fertilizer stores) to the
raw plaster mix.

Somewhat
more water than is used for traditional cement stucco was needed in order to keep
the pumper/mixer and supply hose from clogging up. Picture below -- grumbling
stucco crew getting their pumper unclogged.

Cracking

We
had some cracking as the stucco started to cure. This was easily repaired with
a wet float sponge before the plaster was dry. A warm (but not hot) and humid
environment is best to allow the stucco to cure slowly and not dry out too quickly.

General
Cautions

Lime
is very alkaline and caustic -- producing a terrific case of "dishpan hands"
in just a few minutes. Don't breath the dust as you shovel it or get it in your
eyes. Wearing gloves, a dust mask, and eye protection is highly recommended. Also
the ferrous sulfate not only stains plaster, it stains your hands so wear gloves.